Salivary nitrate from dietary or endogenous sources is reduced to nitrite by oral bacteria. In the acidic stomach nitrite is further reduced to bioactive nitrogen oxides including NO. In this study we investigated the gastro-protective role of nitrate intake and of luminally applied nitrite against provocation with diclofenac and taurocholate. Mucosal permeability (⁵¹Cr-EDTA clearance) and gastric mucosal blood flow (laser-Doppler flowmetry) were measured in anesthetized rats, either pretreated with nitrate in the drinking water or given acidified nitrite luminally. Diclofenac was given i.v. and taurocholate luminally to challenge the gastric mucosa. Luminal NO and nitrite content in the gastric mucus were determined by chemiluminescence. The effect of luminal administration of acidified nitrite on the mucosal blood flow was also investigated in eNOS-deficient mice. Rats pretreated with nitrate or given nitrite luminally had higher gastric mucosal blood flow than controls. Permeability increased more during the provocation in the controls than in the nitrate- and nitrite-treated animals. Dietary nitrate increased luminal NO levels 50 times compared to controls. Nitrate intake also resulted in nitrite accumulation in the loosely adherent mucus layer and after removal of this mucus layer blood flow was reduced. Nitrite administrated luminally in eNOS-/- mice increased mucosal blood flow. We conclude that dietary nitrate as well as direct luminal application of acidified nitrite decrease diclofenac- and taurocholate-induced mucosal damage. The gastro-protective effect likely involves a higher mucosal blood flow caused by non-enzymatic NO production. These data suggest an important physiological role of nitrate in the diet.